Behind the scenes

Dumbledore is also able, if not to speak, then at least to understand, Parseltongue when spoken. Although it seems unlikely, it is possible one can learn the language of the serpents on the school, as Dumbledore must have picked it up somwhere, and that Parsletounge indeed is a extraordinary language. Although, if this was the case, it is highly unlikely that many would attend the class, due to its dark reputation and connection to the Dark Arts.